#include<stdio.h>

struct square {
    int length;
    int width;
};

int area(struct square s); // 

int main() {
    struct square square = {20, 10};
    // pass structure to function
    printf("area : %d\n", area(square)); // area : 200
    // printf("original length : %d\n", square.length); // 20
    return 0;
}

int area(struct square s) {
    // s.length = 10; // not modify the original length
    return s.length * s.width;
}